Computer-based navigation systems for use on land have become available in a variety of forms and provide a variety of useful features. These types of navigation systems can be used to display maps, provide route guidance, or to help a user find locations of specific restaurants, hotels, airports, and shopping centers, for example.
These navigation systems use data that represent the geographic features located in a region. The geographic features that are represented include the road network located in the region, intersections, points of interest (such as hotels, gas stations, ATMs, government buildings, etc.), lakes, golf courses, and so on.
In some geographic databases, each road is represented as one or more discrete road segments, each of which is represented by a separate data entity. A representation of a road segment includes, among other things, information about its location (i.e., latitude, longitude, and possibly altitude) and shape. If a road segment is straight, it can be represented by identifying its endpoints. However, if a road is other-than-straight, additional information is required to indicate the shape of the road.
One way to represent the shape of an other-than-straight linearly extending feature, such as a road segment, is to use shape points. Shape points are points through which a road segment passes between its end points. By providing the coordinates of one or more shape points, the shape of an other-than-straight road segment can be represented.
There are other ways of representing other-than-straight linearly extending features. For example, linearly extending features may be represented using mathematical expressions, such as splines. Use of mathematical expressions, such as splines, may provide for a smooth and possibly more realistic way to represent linearly extending geographic features.
Although use of mathematical expressions, such as splines, provides advantages, there is still room for improvement. One consideration associated with the use of splines, or other mathematical expressions for representing linearly extending geographic features, relates to the representation of intersections. Where two road segments, each represented by separate splines, connect to each other end to end, the spline that represents one of the road segments may not necessarily align with the spline that represents another road segment. In other words, there may not necessarily be a smooth transition between the splines that represent road segments that connect to each other end to end. This may occur even if the actual road segments in the real world connect to each other with a smooth transition.
Accordingly, it is an objective to represent geographic features, such as road geometry, in a way that provides smooth curve geometry at intersections.